Polymeric oxide lubricant containing organic disulfide



Patented Aug. 29,1950

POLYMERIC OXIDE LUBRICANT CONTAIN .ING ORGANIC DISULFIDE William E. Vaughan and Denham Harman, Berkeley, Calii'., assignors to Shell Development Company, San Francisco, Calif a corporation of Delaware No Drawing. Application October 28, 1946, Serial No. 706,097

Claims. (01. ass-48.2)

I This invention relates to novel lubricating compositions. More particularly, it pertains to certain fractions of non-mineral oil base sulfurcontaining compounds, which are, especially suitable for low temperature or extreme pressure lubrication.

The use of mineral oil fractions for lubricating is suitable for many purposes, but it is well known that such lubricants possess certain inherent limitations, such as tendency to oxidize, thicken-. ing at low temperatures, etc. A large number of additives have been employed with mineral oils in order to improve these shortcomings. To a certain degree, the resulting compositions may -be used successfully for most lubricating purposes.

' Various synthetic lubricants have been proposed from time to time. These include polymers of cracked wax oleflns, alkylated aromatics such as alkylated naphthylenes, and so on. Some of these are useful for special purposes, but, especially if the previously known synthetic lubricants were derived from olei'lnic sources, they usually possessed corrosion and oxidation characteristics limiting their utility to a substantial degree.

TAnother type of synthetic lubricant which has been investigated is the alkylene oxide polymer type, such as polymerized propylene oxide. Such polymers are useful under mild operating conditions.

' Organic disulfides, such as dimethyl disulfide, are known, but the possible use of certain classes ofthem as lubricants has not previously been proposed. Furthermore methods for the formation of such disulfides have been descr bed, but heretofore'the adjustment of such methods for the preparation of disulfides having lubricating properties has not been suggested.

It is an object of the present invention to provide a novel method for the production of a nonhydrocarbon lubricant. It is another object of the present invention to provide a novel method for the preparation of a lubricant useful at low temperatures. It is still another ob ect of this invention to provide a novel method for the preparation of a lubricant possessing inherent extreme pressure properties. It is a further object of the present invention to provide synthetic lubricants Y derived from mixtures of mercaptans. It is yet another object of the present invention to utilize petroleum by-products. Another object is the provision of extreme pressure additives for other lubricants. Other objectswill become evident from the following disclosure.

2 Now, in accordance with this invention, it has been found that lubricants having inherent extreme pressure properties may comprise organic disulfides having the general configuration wherein R is an organic radical, and each X is a substituent such as a hydrogen atom, hydrocarbon radical or acyl group, especially if the disulfide or a mixture thereof has a minimum boiling point above about C. at 0.2 cm. mercury pressure. Still in accordance with this invention, it has been found that, not only may such disulfides be used without modification as extreme pressure lubricants, but that they may be employed as extreme pressure additives for other lubricants. Disulfides satisfactory for such uses may be prepared, according to the present invention, by forming the metallic salts of a mercaptan, or mixture of mercaptans, oxidizing the salt, and removing the more volatile fraction of theproduct,

which essentially is a disulfide or mixture of disulfides.

The mercaptans from which the subject lubricants may be prepared are those having the general formula wherein X is a substituent such as a hydrogen atom, a hydrocarbon group or an acyl radical, and R1 is a hydrocarbon radical, preferably an alkylene radical. These include for example mercaptoethyl alcohol, mercaptopropyl alcohol, mercaptobutyl alcohol, mercaptoamyl alcohol, mercaptohexyl alcohol, mercaptoheptyl alcohol, mercaptooctyl alcohol, mercaptononyl alcohol, mercaptodecyl alcohol, mercaptododecyl alcohol, etc. wherein the sulfhydryl and hydroxyl groups are at opposite ends of the hydrocarbon chain.

Although such a configuration is preferred for the preparation of the present disulfide lubricants, alternative configurations include those in which the hydrocarbon is highly branched and/or in which the sulfhydryl group or the hydroxyl group (or both) is not on a terminal carbon atom.

Mercaptoalkyl alcohols having the latter type of configuration include 1-hydroxy-3-mercaptobutane, 2-hydroxy-4-mercaptobutane, z-hydroxyfi-mercaptopentane, 3-hydroxy-4-mercaptopentane, 1-hydroxy-4-mercaptohexane, 2-hydroxyfi-mercaptohexane, S-hydroxy-"l-mercaptodecane, l-hydroxy-S-methyl 6 mercaptohexane, l-hydroxy-i-isopropyl-S-mercaptohexane, and their homologs and analogs.

1 preferably in the presence of water.

; oxides, carbonates and hydroxides are, for ex- 1 ample, those of the alkali metals and the alkaline I earth metals, and include lithium, sodium, po-

, tassium, calcium, strontium and barium oxides, i

carbonates and hydroxides.

The ethers of neercapto alcohols which form I satisfactory disulfide lubricants have the general configuration saturated hydrocarbon. These include such The metal salts are conveniently prepared by dissolving the metal compound in water and ethers as 1-mercapto-4-methoxybutane, l-mer- 3 capto-5-ethoxypentane, 1-mercapto-4-ethoxybu tane, 1-mercapto-6-metahoxyhexane, l-meroapto-fi-ethoxyhexane, l-mercapto-G-propoxyhexane, etc. Such ethers may have branched hy- Other ethers which may be used to form satis- 1 factory disulfide lubricants include those in which 1 the mercapto group and/or the alkoxy group are attached to carbon atoms other than terminal carbon atoms.

These are illustrated by such ethers as 1-mercapto-2-methoxypropane, l-mercapto-3-ethoxybutane, 1-mercapto 4 propoxylhexane, 1-merc apto-5-butoxydecane, B-mercap- 1 to-3-methoxypropane, '3-mercapto-4-ethoxybuf tane, 4-mercapto-5-propoxypentane, Z-mercapto- 3 methoxybutane, 3-mercapto-fi-ethoxyhexane, Z-mercapto-B ethyl-4-methoxypentane, etc.

Esters of mercapto alcohols likewise may be used for the formation of the disulfide lubricants described herein. These have the general formula I wherein R4 and Rs are hydrocarbon, especially alkyl, radicals. Preferred esters having the I drocarbon radicals. For example, suitable ethers of this type are l-mercapto-2-ethyl-3-methoxyjpropane, 1-mercapto-3-methyl-4-ethoxybutane, 1-mercapto-3-isopropyl-7-butoxyheptane, etc.

above configuration include those in which the mercapto group and the ester group are attached to terminal carbon atoms of a hydrocarbon. The esters from which the most satisfactory disulfide lubricants are prepared are those in which R1 is The esters may have other configurations wherein the sulfhydryl group, the ester group or i an alkyl group is attached to carbon atoms which are not terminals of a hydrocarbon chain. Typical esters having such configurations are l-mercapto 2 methoyloxypropane, l-mercaptoi- 3 ethoyloxyhexane, 2 mercapto-3-propoyloxyproi pane, 3 mercapto-5-ethoyloxypentane, Z-mercapto-3-methoyloxybutane, 2-,mercapto-5-methoyloxyhexane, l-mercapto-2-methyl-3-methoyloxypropane, etc.

As noted hereinbefore, the disulfide lubricants may be prepared by oxidizing a metallic salt of the mercaptan. The metal salt is conveniently formed by treatment of mercaptans such as those I These include such above with a. normal metallic oxide or hydroxide,

Suitable adding the mercaptan (or mercaptans) thereto. Thismay be done at room temperature, but other temperatures from about 10 C. to about C. may be employed. The reaction is quantitativeand usually proceeds substantially instantaneously, although some of the less active mercaptans may require a more prolonged periodto allow complete transformation of the mercaptans to the metallic salt.

Following the completion of the above reaction, the salts so formed areoxidized to form the disulfide. This may be done conveniently in the same alkaline medium in which the salt was formed, an excess of alkali being present. Alternatively, the salt may be isolated and subsequently placed in another medium for treatment with oxidizing agents. Preferably any medium used is alkaline, and may be made so with inorganic alkalies, such as those described above. Alternatively the oxidation may be conducted in the presence of anorganic base, such as primary, secondary or tertiary amines, pyridine, piperidine or quaternary ammonium bases or their salts. The medium may be aqueous or organic, such as alcoholic.

The oxidation of the metallic salt of the mercaptan is effected by use of oxidizing agents such as air, oxygen, ozone, iodine, bromine, chlo-' rine, hydrogen peroxide, organic peroxides, permanganate, dichromate, etc. The reaction usually is conducted by gradual addition of the oxidizing agent to a suspension or solution of the mercaptan salt. This is done conveniently starting at room temperature, although temperatures between about -40 C. to about 150 C. may be used, dependent upon the reactivity of the oxidizing agent and the mercaptan salt. The addition of the oxidizing agent may be conducted at a relatively rapid rate if temperature control methods are employed. Preferably, however, theaddition is conducted over a more extended period, thatis, from about one to about fortyeight hours. With such reactive mercaptan salts as the potassium salt of amma-mercaptopropyl alcohol, the reaction is complete in two to eight hours, when iodine is the oxidant. the reaction temperature being about 20-30" C. An equivalent amount of the oxidizing agent, or an excess thereof, must be used in order to obtain complete oxidation of'the salt to the disulfide.

An essential feature of the present invention is the substantially complete removal of volatile components from the product. This is especially important when mixtures of mercaptans, such as those derived from petroleum sources, are used for the preparation of the disulfide. Such mixtures may include inert volatile material or lower mercaptans which form disulfides having too high a volatility to be useful for most lubrieating purposes. The source of merca tans and their configurations will have'a great effect upon the proportion of relatively volatile components in the product.

The fraction of relatively volatile constituents removed will depend upon the lubricating purpose for which the remainder will be employed. If no fraction is removed the composite product is generally useless as a lubricant, since the lighter fractions will inevitably volatilize during operation to a greater or less degree dependent upon the conditions to which it is subjected. However, for general lubricating purposes, the fraction volatilizing below about C. at 0.2

assoms .cm. mercury pressure is preferably removed, and generally, that fraction volatilizing below about 120C. at 0.2 cm. mercury pressure is removed in order to obtain a lubricant having optimum properties.

The product may be further treated to remove color or alter configuration. For example, instead of forming bis(alkoxyalkyDdisuliides or bis(alkoyloxyalkyDdisulfldes from the corresponding mercaptans, as described above, bis(hydroxyalkyl) disulildes may be prepared from the corresponding mercaptan, after which the disulflde may be etherifled or esterii'ied.

Various etherifying agents maybe used for etherifying terminal hydroxyls. These include alkyl halides, such as methyl iodide, methyl bromide, ethyl chloride, propyl iodide; aralkyl halides such as benzyl chloride and methylbenzyl chloride; hydroxyalkylchlorides such as hydroxyethyl chloride; carboxyalkylating agents such as sodium monochloracetate; and alkylene halides such as allyl chloride. Ordinarily, the etherification is carried out in strongly basic environments; sodium hydroxide, liquid ammonia and quaternary ammonium bases and salts being the usual basic substances present.

Esteriflcation of the terminal hydroxyls may be accomplished with various inorganic groups such as nitrates, phosphates or sulfates. However, preferred esterifying agents are the organic acids anhydrides or acid chlorides, and especially fatty acid anhydrides and their chlorides, including for example formic, acetic, propionic, butyric, hexoic, 2-ethylhexoic, and higher fatty acids such as lauric, stearic, myristic, palmitic and capric acids. Usually, the esters are formed by treatment of the hydroxylated disulfide with the anhydride of the acid in the presence of a catalyst such as sulfuric or phosphoric acid. The saturated fatty acids form the most stable esters with the bis(hydroxy alkyl) disuifldes.

At times it is preferable to allow only partial etherification, thus forming half-ethers or halfesters instead of the di-ethers or di-esters theoretically possible. For other purposes the endgroup hydroxyls may not only be partially or completely esterified or etherifled, but also may be so treated as to result in the formation of mixed ethers, mixed esters or ether-esters.

The disulfide lubricants comprise one or more compounds having the general configuration wherein X is a substituent such as a hydrogen atom, hydrocarbon radical or acyl group, and each R is an organic radical, especially a hydrocarbon radical. It will be noted that disulfldes having ether or ester end-groups may be formed from mercapto alkyl alcohols, etherification or esterification being effected subsequent to the formation of the disulilde, or they may be formed by oxidation of salts of mercapto-ethers or esters.

acteristics, oxidation resistance, extreme pressure characteristics and lubricating properties which make them especially useful for lubricating purposes, either by themselves or in combination with other lubricants or lubricant additives.

The disulflde lubricants have pour points which make them useful over wide temperature ranges, some of them being particularly useful as low temperature lubricants, since they may have pour points as low as -65 'F. or even lower. This property will depend to a certain extent on the molecular weight of the radicals attached to the disulflde group, and partly upon the structure of such radicals.

The disulilde lubricants have viscosities which vary over a considerable range, commonly being from about '10 to 500 centistokes at 100 F., and from to 75 centistokes at 210 F. These viscosities correspond approximately to SAE 10-80 lubricating oils.

The resistance of the disulflde lubricants to oxidation and their response to oxidation inhibitors is outstanding. In this regard, one feature of the oxidation of the disulflde lubricants is that their. products of oxidation are more or less volatile, and eventually tend to escape from the lubrication system, thus promotk This phenomenon is vmonocyclic aminophenols, etc.

The outstanding properties of the disuiilde lubricants is their superior performance as extreme pressure lubricants. This property is evident when the disulfldesare used along or when they are employed as extreme pressure additives for other lubricants such as mineral oils, polymers of alkylene oxides and glycols, polyamides,

Typical disulfide lubricants include one or more polymeric siloxanes, etc. The extreme pressure characteristic is especially outstanding when the blends of the disulfides and other lubricants contain from about 3 to 50% of the disulfides.

The disuliide lubricants may contain other substances to modify their properties, such as corrosion inhibitors (especially organic monobasic and polybasic acids which'are capable of forming water-insoluble metallic salts), gelling agents for the formation of greases, etc. The lubricant compositions are useful as or in cutting oils as well as in engine lubricants.

Having described the preparation, properties and uses of the disulflde lubricants, illustrative examples are presented:

EXAMPLEI- Preparation of bis(gamma-hydrorypropyl) disulfide Ninety-two parts gamma-mercaptopropyl alcohol were treated with 56 parts potassium hydroxide in aqueous solution. To the solution of the potassium salt so formed, 126 parts iodine were added dropwise, starting at room temperature. The product so formed was water-washed and unreacted material was removed by fractional distillation in order to recover bis(gammahydroxypropyl) disulflde.

The disulflde was used as an extreme pressure additive, as described in Example II.

EXAIVIPLE 11 Use of disulfide as an extreme pressure agent The extreme pressume characteristics of the disulfide prepared as described in Example I were tested, using the 4-ball machine described by Boelage in .Engineering, July 14, 1933. ;The tests comprise determining the wear caused by use of a propylene oxide polymeric lubricant, both in the presence and absence of the disulfide. The results obtained are given below. The conditions used were one minute at 1500 R. P. M. under the indicated loads.

We claim as our invention I 1. A lubricating composition comprising a major amount of an oleaginous alkylene polymeric oxide material and a, minor amount sufficient to impart extreme pressure properties of an organic disulfide having the general configuration: XOR-SSR-OX, wherein each R is a saturated alkylene radical and each X is a substituent' of the group consisting of hydrogen atoms, saturated alkyl radicals and saturated acyclic acyl groups having up to eighteen carbon atoms, said disulfide being prepared by dispersing a mercapto alkyl monohydric alcohol in an alkaline medium, oxidizing saidalcohol with a peroxide. removing from the product the portion volatilizing below about 140 C. at 0.2 cm. mercury pressure to obtain the organic disulfide residue.

2. A lubricating composition comprising a major amount of an oleaginous alkylene polymeric oxide material and a minor amount suillcient to impart extreme pressure properties of an organic disulfide having the general configuration: XOR--SSR-OX, wherein each R is a saturated alkylene radical and each X is a substituent of the group consisting of hydrogen atoms, saturated alkyl radicals and saturated acyclic acyl groups having up to eighteen carbon atoms, said disulfide being prepared by dispersing a mercapto alkyl monohydric alcohol in an alkaline medium, oxidizing said alcohol with a halogen, removing from the product the portion volatilizing below about 140 C. at 0.2 cm. mercury pressure to obtain the organic disulfide residue.

3. A lubricating composition consisting essentially of an oleaginous propylene oxide polymer and as an extreme pressure agent therefor from 0.62 to 3.2% by weight of bis(gamma-hydroxypropyl)' disulfide, which disulfide has a boiling point of at least about 140 C. at 0.2 cm. mercury pressure.

4. A lubricating composition consisting essentially of an oleaginous alkylene polymeric oxide material and a minor amount sufllcient to impart extreme pressure properties of bis(beta-hydroxyethyl) disulfide, which disulfide hasa boiling point of at least, about C. at 0.2 cm. mercury pressure.

5. A lubricating composition consisting essentially of an oleaginous allrylene polymeric oxide material and a minor amount suiflcient to impart extreme pressure properties of bis(gamma-hydroxypropyl), disulfide, which disulfide has boiling point of at least about 140 C. at 0.2 c mercury pressure.

6. A lubricating composition consisting essentially of a alkylene polymeric oxide material and a minor amount sumcient to impart extreme pressure properties of an organic disulfide residue having the general configuration:

wherein A1 and A: are saturated acyclic acyl groups having up to eighteen carbon atoms and R1 and R2 are saturated alkylene radicals, said disulfide being prepared by dispersing a mercapto alkyl monohydric alcohol in an alkaline medium, oxidizing said alcohol, and removing from the product the portion volatilizing below about 140' C. at 0.2 cm. mercury pressure to obtain the organic disulfide residue.

7. A lubricating composition consisting essen tially of an oleaginous alkylene polymeric oxide material and a minor amount sumcient to impart extreme pressure properties of an organic disulflde residue having the general configuration: RiOR2SS--Ra-OR4, wherein R4 and R4 are saturated alkyl radicals having up to tour carbon atoms and R2 and R3 are saturated alkylene radicals, said disulfide being prepared by dispersing a mercapto alkyl monohydric alcohol in an alkaline medium, oxidizing said alcohol, and removing from the product the portion volatilizing below about 140 C. at 0.2 cm. mercury pressure to obtain the organic disulfide residue.;

8. A lubricating composition consisting essentially of an oleaginous alkylene polymericbxide material and a minor amount suflicint to impart extreme pressure properties of an organic disulfide residue having the general configuration: HOR1SSR2OH, wherein R1 and R: are saturated alkylene radicals, said disulfide being prepared by dispersing a mercapto alkyl monohydric alcohol in an alkaline medium, oxidizing said alcohol, and removing from theproduct the portion volatilizing below about 140 C. at 0.21pm. mercury pressure to obtain the organicdisulflde residue. I 9. A lubricating composition consistin'g'essentially of a major amount of anoleaginous' alkylene polymeric oxide material and a minor amount sufilcient to impart extreme pressure properties of an organic disulfide residue having the general configuration: X0'RSS -R"Ox, wherein each R is a saturated alkylene radical and each X is a substituent of the group consisting of hydrogen atoms, saturated alkyl radicals and saturated acyclic acyl groups having up to eighteen carbon atoms, said disulfide being prepared by dispersing a mercapto alkylmonohy- 'dric alcohol in an alkaline medium, oxidizing,

said alcohol, and removing from the product the portion volatilizing below about 140 C. at 0.2,cm. mercury pressure to obtain the organic disulfide residue. .10. A lubricating composition consisting essentially of a major amount of an oleaginous propylene oxide polymer and a minor amount suflicient to impart extreme pressure properties of an'organic disulfide residue of the group consisting of bis(hydroxy alkyl) disulfldes having the general configuration: wherein 7 R is a saturated alkylene radical, said disulfide being prepared by dispersing a mercapto alkyl acyl groups of said esters having up to 18 carbon 5 atoms, said residue having removed therefrom any portion volatilizing below 140 C. at 0.2 cm.

mercury pressure.

WILLIAM E. VAUGHAN. DENHAM HARMAN.

10 REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,001,715 Fischer May 21, 1935 2,174,248 Mikeska et a1. Sept. 26, 1939 2,246,712 Barth June 24, 1941 2,293,868 Toussaint Aug. 25, 1942 2,378,576 Okitg, June 19, 1945 2,415,002 Bruson Jan. '28, 1947 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR AMOUNT OF AN OLEAGINOUS ALKYLENE POLYMERIC OXIDE MATERIAL AND A MINOR AMOUNT SUFFICIET TO IMPART EXTREME PRESSURE PROPERTIES OF AN ORGANIC DISULFIDE HAVING THE GENERAL CONFIGURATION: XO-R-S-S-R-OX, WHEREIN EACH R IS A SATURATED ALKYLENE RADICAL AND EACH X IS A SUBSTITUENT OF THE GROUP CONSISTING OF HYDROGEN ATOMS, SATURATED ALKYL RADICALS AND SATURATED ACYCLIC ACYL GROUPS HAVING UP TO EIGHTEEN CARBON ATOMS, SAID DISULFIDE BEING PREPARED BY DISPERSING A MERCAPTO ALKYL MONOHYDRIC ALCOHOL IN AN ALKALINE MEDIUM, OXIDIZING SAID ALCOHOL WITH A PEROXIDE, REMOVING FROM THE PRODUCT THE PORTION VOLATILIZING BELOW ABOUT 140*C. AT 0.2 CM. MERCURY PRESSURE TO OBTAIN THE ORGANIC DISULFIDE RESIDUE. 